1. Field of the Invention
The present invention relates to a butterfly damper for a loudspeaker, and especially to a high-input type butterfly damper.
2. Description of the Related Art
The conventional butterfly damper 7 has a structure having an inner circumferential frame 9, an outer circumferential frame 8 and arm members 10 for connecting the inner circumferential frame 9 and the outer circumferential frame 8 to each other, as shown in FIG. 5. The arm member 10, which has a trapezoidal cross section as shown in FIG. 6, is formed by the injection forming, facilitating formation of the arm member. A voice coil is inserted into the inner circumferential frame 9. The outer circumferential frame 8 is fixed to the other structural component (for example, a framework of the loudspeaker). Excitation of the voice coil causes the inner circumferential frame 9, which is supported by means of the arm members 10 having flexibility, to vibrate together with the voice coil.
The conventional butterfly damper 7 however has a problem that amplitude increased by inputting a high input signal causes stress concentration in the arm member 10, resulting in a state in which the arm member 10 is not able to bear the stress, leading to its breakage or occurrence of rupture. The conventional butterfly damper 7 is not adaptable to the high input signal in this manner.
An object of the present invention is therefore to provide a butterfly damper, which has a shape feature by which stress can be distributed and reduced, thus permitting to bear a high input signal.
In order to attain the aforementioned object, a butterfly damper according to the first aspect of the present invention comprises:
an inner circumferential frame;
an outer circumferential frame; and
at least one arm member having one end connected to said outer circumferential frame and an other end connected to said inner circumferential frame,
characterized in that:
said at least one arm member has a racetrack-shaped cross section.
In the present invention, the xe2x80x9cracetrack-shapedxe2x80x9d cross section means an oval cross section having curved corners with a prescribed radius of curvature like an athletic racetrack, without forming any sharp edges. According to the first aspect of the present invention, the arm member has the racetrack-shaped cross section so as to prevent concentration of stress. The radius of curvature of the racetrack-shaped cross section may vary within the prescribed range by which the stress concentration can be prevented.
In the second aspect of the present invention, each of the one end and the other end of the at least one arm member may have at least one curved surface. According to the second aspect of the present invention, the curved surface is formed at each of the opposite ends of the arm member, which connects the inner circumferential frame and the outer circumferential frame to each other, in the vicinity of which stress concentration tends to occur. It is therefore possible to distribute stress, which is to be applied to the adjacent portion of the arm member as connected, to the end thereof, thus reducing the load of stress and preventing occurrence of fissures or cracks.
In the third aspect of the present invention, a plurality of arm members may be provided as the at least one arm member. According to the third aspect of the present invention, it is possible to make a change in length, width and the other conditions of the arm member to the optimum values in accordance with a level of an input signal value and a size of the butterfly damper. Selection of the appropriate values for these conditions may lead to variation in the number of the arm members. There is no limitation in the number of the arm members.
In the fourth aspect of the present invention, the inner circumferential frame, the outer circumferential frame and the at least one arm member may be formed of resin integrally with each other by an injection forming. According to the forth aspect of the present invention, utilizing the injection forming makes it possible to manufacture the integrally-formed butterfly damper in an easy manner. In the present invention, change in shape of the damper suffices to improve only performance of it without increasing a cost.
In the fifth aspect of the present invention, there may be adopted a structure in which the outer circumferential frame (2) has opposite end surfaces and an inner peripheral surface, the inner peripheral surface being connected to the opposite end surfaces to form opposite connecting edge portions; and the one end of the at least one arm member (4) is connected to a portion of the inner peripheral surface of the outer circumferential frame (2), the portion excluding the opposite connecting edge portions. According to the fifth aspect of the present invention, the one end of the at least one arm member is connected to a portion of the inner peripheral surface of the outer circumferential frame, which excludes the opposite connecting edge portions. Even when operation of the damper causes the inner circumferential frame to oscillate, the above-mentioned portion of the inner peripheral surface of the outer circumferential frame serves as a blocking wall for preventing the arm member from oscillating excessively, thus reducing stress.